Getter compositions reactivatable at low temperature after exposure to reactive gases at higher temperature

ABSTRACT

Compositions containing non-evaporable getter alloys are provided which, after having lost their functionality in consequence of exposure to reactive gases at a first temperature, can then be reactivated by a thermal treatment at a second temperature that is lower than the first temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/IT2003/000522, filed Aug. 28, 2003, which was published in theEnglish language on Mar. 25, 2004, under International Publication No.WO 2004/024965 A2 and the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention is directed to compositions containingnon-evaporable getter alloys which, after having lost theirfunctionality as a consequence of an exposure to reactive gases at afirst temperature, can then be reactivated by means of a thermaltreatment at a second temperature, lower than the first one.

Non-evaporable getter alloys, also known as NEG alloys, can reversiblysorb hydrogen and irreversibly sorb gases such as oxygen, water, carbonoxides and, in the case of some alloys, nitrogen.

These alloys are employed in a number of industrial applications whichrequire the maintenance of vacuum: examples of these applications areparticle accelerators, X-ray generating tubes, cathode ray tube displaysor CRTs, flat displays of the field-emission type (called FEDs), andevacuated jackets for thermal insulation, such as thermal bottles(thermos), Dewar bottles or pipes for oil extraction and transportation.

NEG alloys can be also employed to remove the above-mentioned gases whentraces thereof are present in other gases, generally noble gases. Oneexample is the use in lamps, particularly fluorescent lamps which arefilled with noble gases at pressures of some tens of hectoPascal (hPa),where the NEG alloy has the function of removing traces of oxygen,water, hydrogen, and other gases, so to keep a suitable atmosphere forthe lamp operation. Another example is the use in plasma displays, wherethe function of the NEG alloy is substantially similar to that carriedout in fluorescent lamps.

These alloys generally have as main components zirconium and/or titaniumand comprise one or more additional elements selected among thetransition metals, Rare Earths or aluminum.

NEG alloys are the subject-matter of a number of patents. U.S. Pat. No.3,203,901 discloses Zr—Al alloys, and in particular the alloy having theweight percent composition Zr 84%-Al 16%, manufactured and sold by theapplicant (SAES Getters S.p.A.) under the trademark St 101; U.S. Pat.No. 4,071,335 discloses Zr—Ni alloys, and in particular the alloy havingthe weight percent composition Zr 75.7%-Ni 24.3%, manufactured and soldby the applicant under the trademark St 199; U.S. Pat. No. 4,306,887discloses Zr—Fe alloys and in particular the alloy having the weightpercent composition Zr 76.6%-Fe 23.4%, manufactured and sold by theapplicant under the trademark St 198; U.S. Pat. No. 4,312,669 disclosesZr—V—Fe alloys, and in particular the alloy having the weight percentcomposition Zr 70%-V 24.6%-Fe 5.4%, manufactured and sold by theapplicant under the trademark St 707; U.S. Pat. No. 4,668,424 discloseszirconium-nickel-mischmetal alloys with optional addition of one or moreother transition metals; U.S. Pat. No. 4,839,085 discloses Zr—V-Ealloys, wherein E is an element selected among iron, nickel, manganeseand aluminum or a mixture thereof; U.S. Pat. No. 5,180,568 disclosesintermetallic compounds Zr₁M′₁M″₁, wherein M′ and M″, being identical ordifferent from one another, are selected among Cr, Mn, Fe, Co and Ni,and in particular the compound Zr₁Mn₁Fe₁, manufactured and sold by theapplicant under the trademark St 909; U.S. Pat. No. 5,961,750 disclosesZr—Co-A alloys, wherein A is an element selected among yttrium,lanthanum, Rare Earths or a mixture thereof, and in particular the alloyhaving the weight percent composition Zr 80.8%-Co 14.2%-A 5%,manufactured and sold by the applicant under the trademark St 787; U.S.Pat. No. 6,521,014 B2 discloseszirconium-vanadium-iron-manganese-mischmetal alloys, and in particularthe alloy having the weight percent composition Zr 70%-V 15%-Fe 3.3%-Mn8.7%-MM 3%, manufactured and sold by the applicant under the trademarkSt 2002 (by MM is meant mischmetal, i.e., a commercial mixture of RareEarths, for example having the weight percent composition 50% cerium,30% lanthanum, 15% neodymium, and the balance 5% of other Rare Earths.

These alloys are used alone or in a mixture with a second component,generally a metal, capable of providing particular characteristics to abody formed with the alloy, such as a higher mechanical strength. Themost commonly used metals for this purpose are zirconium, titanium,nickel, and aluminum. Compositions comprising the cited St 707 alloy andzirconium or titanium are described for example in UK patent GB2,077,487, while in U.S. Pat. No. 5,976,723 are described compositionscontaining aluminum and a NEG alloy of the formula Zr_(1-x)Ti_(x)M′M″,wherein M′ and M″ are metals selected among Cr, Mn, Fe, Co, and Ni, andx is comprised between 0 and 1.

The functioning principle of NEG alloys is the reaction among themetallic atoms on the alloy surface and the absorbed gases, inconsequence of which a layer of oxides, nitrides or carbides of themetals is formed on that surface. When surface coverage is complete, thealloy is inactive for further absorption. Its function can be restoredby a reactivation treatment, at a temperature which is at least the sameand preferably higher than the working temperature.

However, in some cases, it is impossible to treat an alloy for itsactivation or reactivation at a temperature higher than that at which ithas been previously exposed to gases. This is particularly the case foralloys which are used in devices where the space to the kept undervacuum or a controlled atmosphere is defined by walls made of glass,such as CRT-type screens, flat displays which are either field emissiondisplays or plasma display panels, and lamps. The manufacture of thesedevices generally provides for the getter alloy to be inserted in itsfinal position when the device is still open and its inner space isexposed to the atmosphere. Thereafter, the device is sealed by aso-called “frit-sealing” step, wherein a low-melting glass paste isplaced between two glass portions to be welded together, is brought toabout 450° C., melts, and thus joins the two portions. The vacuum or thecontrolled atmosphere can be obtained in the inner space of the devicebefore sealing (in the so-called “in chamber” process, wherein thedevice assembling steps are carried out in an enclosure under vacuum orcontrolled atmosphere) or, more commonly, after the frit-sealing, bymeans of a “tail”, i.e., a small glass tubule admitting to the space andsuitable for connection to a pumping system. In the case of devicescontaining a controlled atmosphere, such as plasma displays and somelamps, the tail is used also for filling with the desired gases.Finally, the device is sealed by closing the tail, usually by heatcompression. In any case, during frit-sealing, the NEG alloy is exposedto an atmosphere of reactive gases, namely to the gases released by thelow-melting glass paste in the case of “in chamber” processes, and tothese same gases plus atmospheric gases in the case of “tail” processes.The contact between the alloy and the reactive gases occurs at atemperature depending on the process. The device can be homogeneouslybrought to the frit-sealing temperature within a furnace, in which casethe NEG alloy will be exposed to the reactive gases at a temperature ofabout 450° C. Alternatively, it is possible to use a localized heating,e.g., by irradiation, in which case the getter temperature during theoperation depends on its distance from the frit-sealing zone. In anycase, during these operations the NEG alloy surface reacts with more orless intensity with the gases being present, with consequent at leastpartial deactivation of the alloy, such that the residual sorptionvelocity and capacity may result in being insufficient for the foreseenoperation in the device. Therefore, there would be required areactivation treatment at a temperature at least equal to, or preferablyhigher than, that of frit-sealing, which is however generallyimpossible, both to prevent a remelting of the frit-sealing paste whichwould endanger the welding seal, and to avoid impairment of themechanical stability of the glassy portions forming the walls of thedevice containing the getter.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide compositionscontaining a non-evaporable getter alloy that, after having lost theirfunctionality in consequence of an exposure to reactive gases at a firsttemperature, can then be reactivated by a thermal treatment at a secondtemperature which is lower than the first one.

This object is achieved according to the present invention with gettercompositions formed of a mixture of powders of:

-   -   a first component being titanium, possibly partially replaced by        nickel and/or cobalt; and    -   a second component being a non-evaporable getter alloy        comprising zirconium, vanadium, iron, and at least one further        component chosen among manganese and one or more elements        selected among yttrium, lanthanum and Rare Earths, wherein the        weight percentage of the elements can vary in the following        ranges:    -   zirconium from 60 to 90%;    -   vanadium from 2 to 20%;    -   iron from 0.5 to 15%;    -   manganese from 0 to 30%; and    -   yttrium, lanthanum and Rare Earths and mixtures thereof from 0        to 10%.

For the sake of clarity, in the remainder of the description and in theclaims, the elements of the group composed of yttrium, lanthanum, RareEarths and mixtures thereof will be referred to as “component A”,according to the definition adopted in U.S. Pat. No. 5,961,750.Preferably, as component A there is used mischmetal, namely, commercialmixtures containing either cerium or lanthanum as the main component anda mixture of other Rare Earths as the balance.

The inventors have found that the compositions of the invention, incontrast to the NEG alloys alone and in contrast to the knowncompositions of a NEG alloy with a metal, can be exposed to reactivegases (such as atmospheric gases) at relatively high temperatures, e.g.,about 450° C., required for the welding by frit-sealing of glassyportions, and then can be fully reactivated by a thermal treatment at alower temperature, so as not to endanger the seal of the glassy weldingor the mechanical strength of the glass portions which are near to thecomposition.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 is a graph showing the sorption curves (sorption speed S vs.quantity Q of gas already sorbed) of two compositions according to theinvention and of a prior art composition.

FIG. 2 is a graph showing the sorption curves (sorption speed S vs.quantity Q of gas already sorbed) of a third composition according tothe invention before and after the frit-sealing;

FIG. 3 is a graph showing the sorption curves (sorption speed S vs.quantity Q of gas already sorbed) of a fourth composition of theinvention before and after the frit-sealing; and

FIG. 4 is a graph showing the sorption curves (sorption speed S vs.quantity Q of gas already sorbed), before and after frit-sealing, of aknown mixture of titanium and a getter alloy.

DETAILED DESCRIPTION OF THE INVENTION

The NEG alloys used in the compositions of the invention comprisezirconium, vanadium, iron and at least one further element selectedbetween manganese and component A. Manganese and component A are notnecessarily in the alternative and may both be present in the alloys ofthe invention.

When the NEG alloy used in a composition of the invention does notcomprise component A, the weight percents of the elements can vary inthe following ranges:

-   -   zirconium from 60 to 90%;    -   vanadium from 2 to 20%;    -   iron from 0.5 to 15%;    -   manganese from 2.5 to 30%.        In this case, a preferred composition is Zr 72.2%-V 15.4%-Fe        3.4%-Mn 9%.

When the NEG alloy used in a composition of the invention does notcomprise manganese, the weight percents of the elements can vary in thefollowing ranges:

-   -   zirconium from 60 to 90%;    -   vanadium from 2 to 20%;    -   iron from 0.5 to 15%;    -   Component A from 1 to 10%.        In this case, a preferred composition is Zr 76.7%-V 16.4%-Fe        3.6%-A 3.3%.

Finally, when the NEG alloy used in a composition of the inventioncomprises both manganese and the component A, the weight percents of theelements can vary in the following ranges:

-   -   zirconium from 60 to 85%;    -   vanadium from 2 to 20%;    -   iron from 0.5 to 10%;    -   manganese from 2.5 to 30%; and    -   A from 1 to 6%.        In this latter case, a preferred composition is Zr 70%-V 15%-Fe        3.3%-Mn 8.7%-A 3%, corresponding to the previously cited alloy        St 2002.

The above NEG alloys may also contain small percentages, generally lowerthan 5%, of other transition elements.

These alloys are generally employed in the form of a powder, having aparticle size between about 10 and 250 μm, and preferably about 128 μm.

Titanium is generally employed in the compositions of the invention inthe form of a powder, having a particle size comprised between about 0and 40 μm. Alternatively, it is possible to use titanium hydride, TiH₂,which during the subsequent thermal treatments releases hydrogen, thusforming titanium “in situ”.

The weight ratio between NEG alloy and titanium can be comprised withinbroad limits, such as between about 1:4 and 4:1, preferably within about1:2 and 2:1, even more preferably in a ratio of about 3:2.

In an alternative embodiment of the invention, titanium may be partiallyreplaced by nickel and/or cobalt. It has been observed that thecompositions of the invention, during frit-sealing, release hydrogen.This can occur because water sorbed during frit-sealing is decomposed bythe material into oxygen and hydrogen (according to a functioningmechanism common to any getter metals and alloys). While oxygen iscompletely retained by the material, hydrogen sorption is an equilibriumphenomenon, so that this element is partially released. In someapplications, hydrogen release is not harmful, and it can even helpavoid oxidation of some parts of the final devices during frit-sealing.There are, however, applications where hydrogen release is undesirableand must then at least be minimized. For instance, during tests carriedout on flat screens to evaluate the activation and sorption propertiesof the compositions of the invention, it has been noted that hydrogenthus released leads to non-homogeneity in the screen brightness. Theinventors have found that the partial replacement of titanium withpowders of nickel and/or cobalt reduces the phenomenon. The powders ofthese two elements are employed with the same particle sizes previouslyindicated for titanium. Substitution can reach up to about 50% by weightof the titanium.

Frit-sealing treatments may be different according to the kind of deviceto be produced and according to the specific working processes adoptedby any manufacturer. During these treatments, duration, temperature andatmosphere to which the getter composition are exposed may vary widely.As a consequence, the degree of interaction of the composition with thegases present during frit-sealing may vary in a broad range. That canlead to non-reproducibility of the gas sorption properties of thecomposition upon subsequent reactivation. In order to avoid thisproblem, it is possible to subject the compositions of the invention toa pre-oxidation treatment under controlled conditions, generally severeenough. For example, a typical treatment can be carried out at 450° C.for 20 minutes in air, thus obtaining a controlled oxidation of thecomposition. By pre-oxidizing the composition under conditions of time,temperature and atmosphere which are at least the same as the mostsevere foreseen for the frit-sealing treatment, it is assured thatduring the actual frit-sealing the further interaction of thecomposition of the invention with the surrounding environment will benil or at least reduced. In this way, a “normalization” of the chemicalcomposition of the composition of the invention, and a consequent higherreproducibility of its gas sorption characteristics after reactivation,is obtained.

The compositions of the invention can be used to produce getter devicesof various shapes, with or without a support.

When the getter device is formed of the composition only, it will begenerally in the form of pellets obtained by compression, pouring themixture of powders into a suitable mold and compressing the same by asuitable punch, with values of pressure applied generally higher than5000 Kg/cm². Compression may be followed by a sintering step, whereinthe pellet undergoes a thermal treatment at temperatures comprisedbetween about 700 and 1000° C. under vacuum or inert atmosphere. Whilein the case of compression only the getter devices have generally theshape of a pellet, and also when sintering is carried out, whichincreases the mechanical resistance of the finished body, other shapescan also be obtained, such as relatively thin tablets.

As an alternative, the getter device comprises powders of thecomposition according to the invention supported on a suitablemechanical substrate, generally of metal. The substrate can be ametallic strip or sheet, in which case the powders of the compositioncan be deposited by cold rolling or screen-printing, followed bysintering. Cold rolling is a well known technique in the field of powdermetallurgy, while the production of deposits of getter material byscreen-printing is disclosed in U.S. Pat. No. 5,882,727. The substratecan also be a container of various shapes, provided with at least anopen portion through which the composition of the invention can comeinto contact with the space from which the gaseous impurities must beremoved, such as a short cylinder wherein the mixture of powders ispoured and in which the mixture is thereafter compressed by a suitablepunch. In the case where the composition of the invention is introducedinto a container, sintering is generally not required.

The invention will be further illustrated by the following examples.These non-limiting examples show some embodiments designed to teachthose skilled in the art how to practice the invention and to representthe best considered mode to carry out the invention. Examples 1 through10 refer to the gas absorption properties of compositions of theinvention and of the prior art, before and after a treatment thatsimulates the frit-sealing process used in the manufacture of manydevices including getter compositions. Example 11 refers to the releaseof hydrogen from some composition of the invention after frit-sealing.

EXAMPLE 1

A pellet having a thickness of 0.5 mm and a diameter of 4 mm isprepared, employing 0.10 g of powdered titanium having a particle sizeof less than 40 μm and 0.15 g of powdered alloy having a weight percentcomposition Zr 70%-V 15%-Fe 3.3%-Mn 8.7%-MM 3% with a particle size ofabout 125 μm. The pellet is produced by compression only under 10,000Kg.

The thus produced pellet is treated in air at 450° C. for 20 minutes tosimulate the conditions of a frit-sealing treatment. The pellet is thenactivated by thermal treatment under vacuum at 350° C. for two hours.

A carbon monoxide (CO) sorption test at room temperature is carried outon the thus-treated pellet, following the procedure described in thestandard ASTM F 798-82, by operating with a CO pressure of 4×10⁻⁵ hPa.The results of the test are graphically shown as curve 1 in FIG. 1, assorption speed (designated as S and measured in cc/s×g, namely cm³ ofgas sorbed in a second per gram of alloy) as a function of the quantityof sorbed gas (designated as Q and measured in cc×hPa/g, namely cm³ ofgas multiplied by the pressure of the measurement in hPa per gram ofalloy).

EXAMPLE 2

The test of Example 1 is repeated, but in this case the pellet issubjected, after its formation by compression, to a sintering treatmentunder inert atmosphere at 870° C. for 40 minutes. A CO sorption test iscarried out on the pellet, the results of which are shown in FIG. 1 ascurve 2.

EXAMPLE 3 (COMPARATIVE)

The test of Example 2 is repeated, employing however a pellet obtainedfrom a composition according to the prior art, formed of 0.10 g ofpowdered titanium and 0.15 g of powder of an alloy having a weightpercent composition Zr 70%-V 24.6%-Fe 5.4%. A CO sorption test iscarried out on the pellet, the results of which are shown in FIG. 1 ascurve 3.

EXAMPLE 4 (COMPARATIVE)

The test of Example 1 is repeated, using however a pellet having aweight of 0.25 g comprised only of powder of the alloy of weight percentcomposition Zr 70%-V 24.6%-Fe 5.4%, already known in this field. A COsorption test is carried out on the pellet. The results of this test arenot shown in the drawing because this pellet has proved to have asorption capacity equal to zero in practice, and therefore the relevantabsorption data were not detectable.

EXAMPLE 5

A pellet having a thickness of 0.5 mm and diameter of 4 mm is prepared,employing 0.10 g of powder of titanium having a particle size of lessthan 40 μm and 0.15 g of powder of an alloy having a weight percentcomposition Zr 72.2%-V 15.4%-Fe 3.4%-Mn 9% with a particle size of about125 μm. The mixture of powders is compressed in a suitable mold under10,000 Kg, and the pellet is then subjected to a thermal treatment ofsintering at 870° C. for 40 minutes under vacuum.

Upon exposure to air (having the effect of passivating the pellet), thethus-produced pellet is activated by thermal treatment under vacuum at atemperature of 350° C. for 2 hours. A carbon monoxide (CO) sorption testat room temperature is carried out on the pellet, as described inExample 1. The results of the test are graphically shown as curve 4 inFIG. 2, as sorption speed (S) as a function of the quantity of sorbedgas (Q).

EXAMPLE 6

The test of Example 5 is repeated with a new pellet, the only differencebeing that after its preparation, the pellet is treated at 450° C. inair for 20 minutes to simulate the conditions of a frit-sealingtreatment. The pellet is then activated by thermal treatment undervacuum at 350° C. for 2 hours. A CO sorption test is carried out on thissecond pellet under the same conditions of the preceding test. Theresults of the test are graphically shown as curve 5 in FIG. 2.

EXAMPLE 7

The procedure of Example 5 is repeated, employing in this case thepellet preparation of 0.15 g of powder of an alloy having the weightpercent composition of Zr 76.7%-V 16.4%-Fe 3.6%-MM 3.3%, wherein MMmeans a mixture of weight percent composition of 50% cerium, 30%lanthanum, 15% neodymium, and the balance 5% of other Rare Earths.

The results of the CO sorption test on this pellet are shown in FIG. 3as curve 6.

EXAMPLE 8

The procedure of Example 6 is repeated, but using a pellet obtained withthe alloy of Example 7.

The results of the CO sorption test on this pellet are shown in FIG. 3as curve 7.

EXAMPLE 9 (COMPARATIVE)

The procedure of Example 5 is repeated, but using 0.15 g of powder of analloy of the weight percent composition Zr 70%-V 24.6%-Fe 5.4% forobtaining the pellet.

The results of the CO sorption test on this pellet are shown in FIG. 4as curve 8.

EXAMPLE 10 (COMPARATIVE)

The procedure of Example 6 is repeated, but using a pellet prepared withthe alloy of Example 9.

The results of the CO sorption test on this pellet are shown in FIG. 4as curve 9.

EXAMPLE 11

This example refers to the release of hydrogen from compositions of theinvention after frit-sealing.

By using compositions of the invention, a series of specimens in theform of pellets of thickness 0.5 mm and diameter 4 mm are preparedfollowing the procedure of Example 1. Weight percentages of thecomponents and pre-oxidation conditions of the specimens are given inthe following table: TABLE 1 Specimen Alloy Ti Ni Co Pre-oxidation 1 6040 / / / 2 60 40 / / air, 450° C., 20′ 3 60 35  5 / air, 450° C., 20′ 460 35 /  5 air, 450° C., 20′ 5 60 30 10 / air, 450° C., 20′ 6 60 30 / 10air, 450° C., 20′

The getter alloy employed is always the one of Example 1, that is, thealloy of weight percent composition Zr 70%-V 15%-Fe 3.3%-Mn 8.7%-NM 3%.Also, particle sizes of powders of the different components are as givenin Example 1 (nickel and cobalt, when present, have the same particlesize as titanium).

Hydrogen content analyses are carried out on the thus-producedspecimens, both on the fresh specimen and after a 20 minute treatment at450° C. in the presence of 1.33 hPa of water vapor. This treatmentsimulates a frit-sealing used by some PDPs manufacturers, which iscarried out under vacuum and in which the atmosphere is essentiallycomposed of the water vapor released by the inner components of thescreen (particularly, the phosphors). The hydrogen content of thevarious specimens is measured with a hydrogen analyzer model RH-402 ofLECO Corp. of St. Joseph, Mich., USA. The tests results are reported inTable 2. The “H_(in)” and “H_(fin)” columns give, respectively, thehydrogen weight percent contained in the specimen before and afterfrit-sealing; the column “ΔH” gives the value of the differenceH_(fin)-H_(in) for each specimen; and the column “Δ weight” gives theweight percent increase of the specimen due to water sorption. TABLE 2Specimen H_(in) H_(fin) ΔH Δ weight Retained hydrogen % 1 0.004 0.2430.239 16.8 12.8 2 0.040 0.063 0.023 7.0 3.0 3 0.013 0.092 0.079 5.4 13.24 0.009 0.068 0.059 3.7 14.4 5 0.002 0.095 0.093 2.8 29.9 6 0.009 0.0810.072 3.8 17.1

Discussion of Results

As appears from comparing the sorption curves shown in FIGS. 1 to 3, thepellets produced with compositions of the invention show good sorptionfeatures upon frit-sealing, even better than those shown beforefrit-sealing.

In particular, FIG. 1 shows that two pellets produced with compositionsof the invention (with and without sintering, curves 2 and 1respectively) show good sorption features upon frit-sealing, as theystill have a sorption speed on the order of 100 cc/s×g after havingalready sorbed a gas quantity of at least 5 cc×hPa/g. In contrast, apellet obtained from a composition of the prior art (curve 3) appears tobe substantially already exhausted upon sorption of less than 0.5cc×hPa/g of CO. A pellet obtained solely from a known alloy (Example 4)no longer has any sorption capacity upon frit-sealing.

FIGS. 2 and 3 show, quite unexpectedly, that the sorptioncharacteristics of the compositions of the invention after frit-sealingare better than those of the same composition before frit-sealing. Incontrast, pellets obtained from a prior art composition show a strongworsening of the sorption features upon frit-sealing (FIG. 4).

These tests also confirm that, in contrast to known compositions, in thecase of compositions according to the invention upon frit-sealing at450° C., it is sufficient to reactivate at a lower temperature (350° C.in the Examples) to obtain good sorption properties again.

The tests described in Example 11 refer instead to the capability ofretaining hydrogen during frit-sealing by different compositions of theinvention. In particular, the relevant data are those reported in Table2. If all of the hydrogen were retained by the specimens, the “ΔH” valuefor each specimen should by equal to 1/9 of the “A weight” value. Inpractice, this doesn't happen, because the before part of hydrogen isreleased. By dividing the value “ΔH” in the column by the value “Aweight” in the column, and then multiplying the result by 100, thepercentage of hydrogen retained by the specimen compared to that sorbedupon water sorption is obtained. The higher the value in the lastcolumn, the better the specimen is from the standpoint of its capabilityof retaining hydrogen. From the results in Table 2, it is seen thatsubstitution of part of the titanium with nickel and cobalt, and inparticular the substitution of 10% by weight of titanium with nickel,allows the hydrogen from the compositions of the invention to besensibly decreased.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A getter composition which is reactivatable by treatment at atemperature lower than that of a previous exposure to reactive gases,the composition comprising a mixture of powders of: a first componentcomprising titanium or a mixture of titanium and at least one of nickeland cobalt, wherein nickel and/or cobalt are present up to 50% by weightof the first component; and a second component comprising anon-evaporable getter alloy comprising zirconium, vanadium, iron, and atleast one further component selected from the group consisting ofmanganese, component A and mixtures thereof, wherein the weightpercentages of elements of the second component are in the followingranges: zirconium from 60 to 90%; vanadium from 2 to 20%; iron from 0.5to 15%; manganese from 0 to 30%; and component A from 0 to 10%; whereincomponent A is selected from the group consisting of yttrium, lanthanum,Rare Earths, and mixtures thereof.
 2. The getter composition accordingto claim 1, wherein the getter alloy further contains up to 5% by weightof other transition elements.
 3. The getter composition according toclaim 1, wherein the getter alloy comprises zirconium, vanadium, iron,and manganese, and the weight percentages of these elements in the alloyare in the following ranges: zirconium from 60 to 90%; vanadium from 2to 20%; iron from 0.5 to 15%; and manganese from 2.5 to 30%.
 4. Thegetter composition according to claim 3, wherein the getter alloy has aweight percent composition of Zr 72.2%-V 15.4%-Fe 3.4%-Mn 9%.
 5. Thegetter composition according to claim 1, wherein the getter alloycomprises zirconium, vanadium, iron, and component A, and the weightpercentages of these elements in the alloy are in the following ranges:zirconium from 60 to 90%; vanadium from 2 to 20%; iron from 0.5 to 15%;and component A from 1 to 10%.
 6. The getter composition according toclaim 5, wherein the getter alloy has a weight percent composition of Zr76.7%-V 16.4%-Fe 3.6%-A 3.3%.
 7. The getter composition according toclaim 1, wherein the getter alloy comprises zirconium, vanadium, iron,manganese and component A, and the weight percentages of these elementsin the alloy are in the following ranges: zirconium from 60 to 85%;vanadium from 2 to 20%; iron from 0.5 to 10%; manganese from 2.5 to 30%;and component A from 1 to 6%.
 8. The getter composition according toclaim 7, wherein the getter alloy has a weight percent composition of Zr70%-V 15%-Fe 3.3%-Mn 8.7%-A 3%.
 9. The getter composition according toclaim 1, wherein the powders of the first component have a particle sizeof up to about 40 μm.
 10. The getter composition according to claim 1,wherein the powders of the second component have a particle sizecomprised between about 10 and 250 μm.
 11. The getter compositionaccording to claim 10, wherein the powders of the second component havea particle size of about 128 μm.
 12. The getter composition according toclaim 1, wherein a weight ratio between the powders of the first andsecond components is comprised between about 1:4 and 4:1.
 13. The gettercomposition according to claim 12, wherein the ratio is comprisedbetween about 1:2 and 2:1.
 14. The getter composition according to claim13, wherein the ratio is about 3:2.
 15. The getter composition obtainedby subjecting the composition of claim 1 to an oxidation treatment. 16.The getter composition according to claim 15, wherein the oxidationtreatment is equal to a frit-sealing treatment foreseen for productionof a device in which the composition will be contained.
 17. The gettercomposition according to claim 16, wherein the oxidation treatmentcomprises exposure to air at 450° C. for 20 minutes.
 18. A getter deviceemploying composition according to claim
 1. 19. The device according toclaim 18, comprising solely powders of the getter composition.
 20. Thedevice according to claim 19, wherein the powders of the gettercomposition have been compressed at a value of pressure higher than 5000Kg/cm².
 21. The device according to claim 20, wherein the compressedpowders have been sintered by thermal treatment at a temperaturecomprised between about 700 and 1000° C. under vacuum or inertatmosphere.
 22. The device according to claim 18, the powders of thegetter composition are supported on a mechanical substrate.
 23. Thedevice according to claim 22, wherein the substrate is a metallic stripor sheet.
 24. The device according to claim 23, wherein the powders havebeen cold-rolled on the metallic strip or sheet.
 25. The deviceaccording to claim 23, wherein the powders of the getter compositionhave been screen-printed on the metallic strip or sheet.
 26. The deviceaccording to claim 22, wherein the substrate is a container providedwith at least an open portion to allow contact between the powders ofgetter composition and a space from which gaseous impurities must beremoved.